They were both raised in the East, which disintegrated in 1989 with the fall of the Berlin Wall.

Mrs Merkel is the daughter of a Lutheran pastor, while Mr Gauck is both a pastor himself and the son of a pastor.

Mr Gauck became interested in politics in the East after his father was deported to Siberia for his civil rights activism.

He became a Lutheran pastor after opting to study theology when other university courses were denied him because of his father's dissidence and because he was not a member of the communist youth organisation.

As a pastor, he held services which preceded the demonstrations that eventually toppled the communist government.

After the fall of the wall, Mr Gauck was made head of the body which investigated the activities of the Stasi, the East German secret police - earning the admiration of all but diehard communists for his work in exposing the crimes of the communist era.

In recent years he has concentrated on campaigning against both left and right extremist threats to Germany's democratic system.

Mr Gauck describes himself as a "liberal left conservative", and has expressed support for the policies of both Social-Democrat and Christian-Democrat coalition governments on a non-partisan basis.

A father of four, he is separated from his wife.

His partner since 2000, the journalist Daniela Schadt, will take on the ceremonial duties of First Lady.